<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    body {
      margin: 0;
      height: 100vh;
      display: flex;
      align-items: center;
      justify-content: center;
      background-color: seagreen;
    }

    .calendar {
      font-size: 8px;
      width: 28em;
      height: 28em;
      background-image: linear-gradient(coral 30%, white 30%);
      box-sizing: border-box;
      border: 1em solid darkslategray;
      position: relative;
      transform: rotate(15deg);
    }

    .calendar::before {
      content: "";
      position: absolute;
      width: 3em;
      height: 4em;
      color: sandybrown;
      background-color: currentColor;
      top: -2em;
      left: 4em;
      border-radius: 100% 100% 50% 50%;
      box-shadow: 0 0 0 1em darkslategray,
      15em 0,
      15em 0 0 1em darkslategray;
    }

    .calendar::after {
      content: "";
      position: absolute;
      width: 3em;
      height: 3em;
      color: silver;
      background-color: currentColor;
      top: 10em;
      left: 4em;
      border-radius: 0.4em;
      box-shadow: 
        0 0 , 5em 0, 10em 0, 15em 0,
        0 5em , 5em 5em, 10em 5em, 15em 5em,
        0 10em , 5em 10em, 10em 10em, 15em 10em;
    }
  </style>
</head>
<body>
  <h1 style="text-align: center; color: coral">日历</h1>
  <figure class="calendar"></figure>
</body>
</html>